Generally, in a construction machine such as a hydraulic excavator, a pilot pressure (oil pressure signal) depending on the operation amount of an operating lever is generated by operation of a mechanical operating lever by the operator. By applying this pilot pressure to a directional control valve, a hydraulic actuator is driven. The method which drives the directional control valve by an oil pressure signal is called “hydraulic pilot type”.
A construction machine is often operated while traveling on a rough road and particularly when passing an obstacle on the road surface, the vehicle body vibrates. At this time, the operator is swung due to vibration of the vehicle body and thus it is difficult to hold the operating lever in a given position, which may cause erroneous operation of the operating lever. Accordingly, the pilot pressure may vary largely and cause jerking.
As a technique for output of a stable operation signal, for example, PTL 1 proposes a method which controls the travel of a vehicle body by processing an electrical pilot type signal waveform. Specifically, the frequency of an electrical operation signal to operate the travel of the vehicle body is attenuated by a band elimination filter process and then the peak frequency is cut by a low-pass filter process to smoothen the operation signal waveform.